(a) Field of the Invention:
The present invention relates to a diaphragm for use in elecro-acoustic transducers such as loudspeakers, headphones, microphones and the like, and more particularly it pertains to a diaphragm utilizing ceramics material as a component of such diaphragm.
(b) Description of the Prior Art:
Diaphragms for use in electro-acoustic transducers such as loudspeaker and comprising a core member with a honeycomb structure are well known. Typically such diaphragm is constructed with a planar-shape honeycomb core member having a skin member adhering to both surfaces of this core member. Known diaphragms of this type use, as a skin member, such material as aluminum, duralumin, glass fiber-reinforced plastics (GFRP), carbon fiber-reinforced plastics (CFRP) and aromatic polyamide fiber-reinforced plastics (for example, a product of Dupont in U.S.A. sold under the tradename of KEVLAR FRP). A skin member made with such material as described above is available at a relatively low price, but it has the drawback that the E/.rho. ratio between Young's modulus E and density .rho. is small. In general, a diaphragm for electro-acoustic transducer is such that the greater the E/.rho. ratio is, the higher will become its resonance frequency, resulting in a widened range of piston motion which is the frequency range of such vibration as will not produce partial vibration of diaphragm, so that the higher will its limit frequency for the reproduction of high-pitch sound, thereby the frequency characteristic of the diaphragm is improved. However, known diaphragms having a honeycomb structure has a small E/.rho. ratio of its skin member, so that they have the drawback that good sound reproduction characteristic cannot be obtained. In case beryllium is used as the material of a skin member, the E/.rho. ratio can be raised. However, because beryllium per se is expensive, there is the problem that a diaphragm using beryllium becomes accordingly high in the cost of manufacture.
By the way, a diaphragm made with a single ceramics material so as to obtain a large E/.rho. ratio and low cost is known. But, such diaphragms are inferior in fragility characteristics. In general, a diaphragm for electro-acoustic transducer with a small thickness and a light weight is preferable because of its superior reproducing characteristic. However, such diaphragms are fragile, so that they must be carefully handled.